This invention relates to carriage-fed sawmill saws.
In the operation of sawmills, it is conventional practice to reduce logs or cants to lumber by placing them one at a time on a sawmill carriage which is reciprocated with respect to a saw. At each pass of the carriage, a board is sawn from the log. This sequence is repeated until the log has been entirely converted to lumber.
The lumber output of the mill obviously is determined by the speed with which the carriage is driven. The faster the drive, the larger the amount of lumber produced in a unit time.
There is a limit, however, to the speed with which the log may be fed to the saw. Sawing too fast causes the resulting lumber to be mis-cut or ruined because the saw will stand only a limited amount of feed. If carried to the extreme, it will damage the saw and may injure the operating personnel.
On the other hand, sawing the log at less than the maximum permissible rate wastes time and lowers production.
The carriage operator thus is faced with a dilemma. If he operates the carriage at too slow a speed, the efficiency of the mill is severely reduced. On the other hand, if he operates the carriage at too rapid a speed, the quality of the lumber product is reduced and damage to the saw may result.
This situation is aggravated by the fact that the logs being fed to the saw vary a great deal in size. The small logs obviously can be sawn at a higher speed, as determined by the speed of the carriage, than can the larger logs.
At the present time there is no way for the carriage operator to know precisely how fast to drive the carriage when processing a sequence of logs of varying diameter, except by the use of his own personal skills and experience. As a consequence, in order to be on the safe side, he tends to drive the carriage at speeds which are below the maximum permissible speed of operation. As noted, this correspondingly cuts down the mill production.
It is the general object of the present invention to provide a visual feed control assembly for carriage-feed sawmill saws which will assist the sawyer in overcoming the foregoing problems and enable him to drive the carriage at its maximum safe speed whatever the size of the logs being processed.
It is a further object of the present invention to provide a sawmill saw control assembly which is accurate, easily and inexpensively installed, easy to maintain, and adaptable for use in any sawmill having an electrically driven saw and associated reciprocating sawmill carriage.
The foregoing and other objects of the present invention are achieved by the provision of a visual feed control assembly comprising in combination an electric-motor-driven sawmill saw, a three-phase electric circuit electrically connected to the saw motor, and first and second trip current relay means each comprising a solenoid and associated switch. A second electric circuit includes first and second electrically operated signal means, e.g. differently colored electric lights.
The solenoid component of the first relay is in series in one of the lines of the three-phase electric circuit while the switch component thereof is in series with the first signal means in the second electric circuit. The solenoid component of the second relay is in series in another of the lines of the three-phase electric circuit while the switch component thereof is in series with the second signal in the second electric circuit.
The first relay is preset to operate at a predetermined minimum saw motor amperage load, thereby energizing the first signal. The second relay is preset to operate at a predetermined maximum saw motor amperage load, thereby energizing the second signal.
When the relays are set at minimum and maximum limits between which the carriage may be operated with maximum efficiency, the operator by simple reference to the signals can determine at what speed to drive the carriage .